Generally, an insulating oil as a cooling medium also serving for insulation is sealed within a tank of a vehicle transformer, and the insulating oil is circulated with an oil feed pump and introduced into a cooling unit provided outside of the tank for cooling. FIG. 9 is a plan view showing a conventional vehicle transformer including such a cooling structure. FIG. 9 is a plan view seen from the floor of a vehicle 31 toward the ground side, and a thick arrow indicates the traveling direction of the vehicle. As shown in the drawing, a transformer main body 32 in which a core and a coil (not shown) are held and an insulating oil is sealed, and a cooling unit 33 for cooling the insulating oil are mounted under the floor of the vehicle 31. An outlet 32b of the insulating oil is provided at one end and an inlet 32a is provided at the other end of the transformer main body 32, and the outlet 32b side is connected to an inlet part of the cooling unit 33 via an oil feed pump 34 and a connecting tube 35 and the inlet 32a side is connected to an outlet part of the cooling unit 33 via a connecting tube 36.
The structure is arranged so that, when the oil feed pump 34 is driven, the insulating oil within the transformer main body 32 may be fed to the cooling unit 33 through the connecting tube 35 and cooled, and pass the other connecting tube 36 and return into the transformer main body 32 again. That is, a one-way channel of the insulating oil (arrows) is formed within the transformer main body 32 (see Patent Document 1, for example).
When the interior of the transformer is cooled with the insulating oil, it is desirable that the insulating oil flows as homogeneous as possible within the tank for raising the cooling efficiency. Typically, in the transformer tank having a rectangular shape, the insulating oil is circulated in the diagonal line direction within the tank. Accordingly, when the cooling unit 33 is provided on one side of the tank, for example, the inlet part of the cooling unit 33 is connected to the outlet 32b provided at the one side of the tank, and the outlet part of the cooling unit 33 is connected to the inlet 32a provided on the opposite side to the one side of the tank via the long connecting tube 36.
The vehicle transformer shown in the above Patent Document 1 is based on the concept, and the inlet 32a and the outlet 32b of the insulating oil are provided in the diagonal line direction of the transformer main body 32 and the inlet 32a side is connected to the outlet part of the cooling unit 33 via the long connecting tube 36 around the side surface of the transformer main body 32.
As described above, in the conventional vehicle transformer, in the connections between the transformer main body 32 and the cooling unit 33, at least one connection needs the long connecting tube 36. Accordingly, there are problems that a space for running the connecting tube 36 is necessary, and the number of parts and the insulating oil within the pipe are increased and the connection work takes a long time.
Patent Document 1: JP-A-11-176650 (page 2 and FIG. 8)